Mechanical and chemical-mechanical planarizing processes (collectively “CMP”) are used in the manufacturing of electronic devices for forming a flat surface on semiconductor wafers, field emission displays and many other microelectronic substrate assemblies. CMP processes generally remove material from a substrate assembly to create a highly planar surface at a precise elevation in the layers of material on the substrate assembly.
FIG. 1 is a schematic isometric view of a web-format planarizing machine 10 for planarizing a microelectronic substrate assembly 12. The planarizing machine 10 has a table 11 with a rigid panel or plate to provide a flat, solid support surface 13 for supporting a portion of a web-format planarizing pad 40 in a planarizing zone “A.” The planarizing machine 10 also has a pad advancing mechanism including a plurality of rollers to guide, position, and hold the web-format pad 40 over the support surface 13. The pad advancing mechanism generally includes a supply roller 20, first and second idler rollers 21a and 21b, first and second guide rollers 22a and 22b, and a take-up roller 23. As explained below, a motor (not shown) drives the take-up roller 23 to advance the pad 40 across the support surface 13 along a travel axis T-T. The motor can also drive the supply roller 20. The first idler roller 21a and the first guide roller 22a press an operative portion of the pad against the support surface 13 to hold the pad 40 stationary during operation.
The planarizing machine 10 also has a carrier assembly 30 to translate the substrate assembly 12 across the pad 40. In one embodiment, the carrier assembly 30 has a head 32 to pick up, hold and release the substrate assembly 12 at appropriate stages of the planarizing process. The carrier assembly 30 also has a support gantry 34 and a drive assembly 35 that can move along the gantry 34. The drive assembly 35 has an actuator 36, a drive shaft 37 coupled to the actuator 36, and an arm 38 projecting from the drive shaft 37. The arm 38 carries the head 32 via another shaft 39. The actuator 36 orbits the head 32 about an axis B-B to move the substrate assembly 12 across the pad 40.
The polishing pad 40 may be a non-abrasive polymeric pad (e.g., polyurethane), or it may be a fixed-abrasive polishing pad in which abrasive particles are fixedly dispersed in a resin or another type of suspension medium. FIG. 2A, for example, is an isometric view of a fixed-abrasive polishing pad having a body 41 including a backing film 42 and a planarizing medium 43 on the backing film 42. The backing film 42 can be a thin sheet of Mylar® or other flexible, high-strength materials. The abrasive planarizing medium 43 generally includes a resin binder 44 and a plurality of abrasive particles 45 distributed throughout the resin binder 44. The planarizing medium 43 is generally textured to form a planarizing surface 46 having a plurality of truncated pyramids, cylindrical columns, or other raised features. The 3M Corporation of St. Paul, Minn., for example, manufactures several fixed-abrasive polishing pads having alumina, ceria or other abrasive particles fixedly bonded to a Mylar® backing film 42 by a resin binder.
Referring again to FIG. 1, a planarizing fluid 50 flows from a plurality of nozzles 49 during planarization of the substrate assembly 12. The planarizing fluid 50 may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the surface of the substrate assembly 12, or the planarizing fluid 50 may be a “clean” non-abrasive planarizing solution without abrasive particles. In most CMP applications, abrasive slurries with abrasive particles are used on non-abrasive polishing pads, and non-abrasive clean solutions without abrasive particles are used on fixed-abrasive polishing pads.
In the operation of the planarizing machine 10, the pad 40 moves across the support surface 13 along the pad travel path T-T either during or between planarizing cycles to change the particular portion of the polishing pad 40 in the planarizing zone A. For example, the supply and take-up rollers 20 and 23 can drive the polishing pad 40 between planarizing cycles such that a point P moves incrementally across the support surface 13 to a number of intermediate locations I1, I2, etc. Alternatively, the rollers 20 and 23 may drive the polishing pad 40 between planarizing cycles such that the point P moves all the way across the support surface 13 to completely remove a used portion of the pad 40 from the planarizing zone A. The rollers may also continuously drive the polishing pad 40 at a slow rate during a planarizing cycle such that the point P moves continuously across the support surface 13. Thus, the polishing pad 40 should be free to move axially over the length of the support surface 13 along the pad travel path T-T.
CMP processes should consistently and accurately produce a uniform, planar surface on substrate assemblies to enable circuit and device patterns to be formed with photolithography techniques. As the density of integrated circuits increases, it is often necessary to accurately focus the critical dimensions of the photo-patterns to within a tolerance of approximately 0.1 μm. Focusing photo-patterns to such small tolerances, however, is difficult when the planarized surfaces of substrate assemblies are not uniformly planar. Thus, to be effective, CMP processes should create highly uniform, planar surfaces on substrate assemblies.
The planarity of the finished substrate surface is a function of several factors, one of which is the distribution of abrasive particles under the substrate assembly during planarization. In certain applications that use a non-abrasive pad and an abrasive slurry, the distribution of abrasive particles under the substrate assembly may not be uniform because the edge of the substrate assembly wipes the slurry off of the pad such that the center region of the substrate assembly does not consistently contact abrasive particles. The center region of the substrate assembly may accordingly have a different polishing rate than the edge region causing a center-to-edge polishing gradient across the substrate assembly.
Fixed abrasive polishing pads, like the one shown in FIG. 2A, are relatively new and have the potential to produce highly planar surfaces. The primary technical advance of fixed-abrasive pads is that the distribution of abrasive particles under the substrate assembly is not a function of the distribution of the planarizing solution because the abrasive particles are fixedly attached to the pad. Fixed abrasive pads accordingly provide a more uniform distribution of abrasive particles under the substrate assembly 12 than abrasive slurries on non-abrasive pads. Fixed-abrasive polishing pads, however, may scratch or otherwise produce defects on the finished substrate surface. The particular mechanism that causes scratching and defects is not completely understood, but it is expected that large pieces 47 of the fixed-abrasive planarizing medium 43 (see FIG. 2) break away during planarization and scratch the substrate assembly 12. Fixed-abrasive pads may also produce defects because, unlike abrasive slurries in which the abrasive particles are mobile and can move with the slurry, the abrasive particles in fixed-abrasive pads do not roll or move with the substrate assembly. As such, minor peaks on the raised features of the planarizing surface 46 or disparities in the size or shape of the fixed-abrasive particles 45 may scratch the substrate surface. Therefore, even though fixed-abrasive pads are promising, they may scratch the finished substrate surface of microelectronic substrate assemblies or otherwise produce defects in the integrated circuits.